It is known that in nuclear reactors there is the need to evacuate the residual heat after the reactor has stopped. For safety reasons, the systems for evacuating the residual heat must be particularly reliable and preferably diversified.
In the past active systems were mostly used, i.e. systems that require electrical energy for operation, whereas today passive systems are increasingly used, i.e. systems that do not require electrical energy for their operation, but nevertheless require the intervention of an operator or control logics and electrical power supplies to become operative.